This invention relates, generally, to an actuator and, more specifically, to an electromechanical hinge-line rotary actuator for use with a thin-wing aircraft in flight-control applications.
Many systems require actuators to manipulate various components. Rotary actuators rotate an element about an axis. In flight-control applications, there has been a trend toward a thinner wing such that size and space are limited at a point of attachment between the wing and an aileron (a wing-control surface) of an aircraft.
This trend has driven use of a rotary actuator of a “hinge-line” design, wherein a rotational axis of the actuator is aligned with that of the aileron and the actuator acts as a hinge (hence, the term “hinge-line”). This trend also raises a need for such an actuator with a tighter cross-section, which limits the diameter of a motor of the actuator, and higher power density.
In turn, torque of the motor is directly related to the motor diameter and current flowing through windings of the motor. However, with the limited motor diameter and an amount of the current being limited to useable amounts on a power bus of the aircraft, an amount of such torque is limited as well. And, since power of the motor equates to speed thereof times the torque amount and this amount is limited, the speed must be higher. Yet, use of the higher-speed motor at the limited torque amount is driving use of higher gear ratios, which makes inertia of the motor a sensitive design parameter.
More specifically, reflected inertia comes into play whenever the motor or a gear set of the aircraft is trying to be back-driven, which is a requirement for a surface of the aileron. And, reduction in the inertia prior to a gear affects the reflected inertia by a factor of a gear ratio squared (for example, a “10:1” gear ratio yields a reflected inertia of 100 times greater than the motor inertia while a “100:1” gear ratio yields a reflected inertia of 10,000 times greater). The inertia also affects responsiveness of the aircraft—i.e., a higher level of the inertia results in a lower responsiveness.
A typical electromechanical hinge-line rotary actuator designed for flight-control applications is arranged to use a conventional motor that is framed (i.e., encased, housed, or mounted) and includes a rotor. The rotor is disposed inside the frame and indirectly connected to an end of a planetary gearbox or gear set through a drive shaft or coupler. In this way, the motor is disposed exterior to and in alignment with the gear set, and there are bearings for the motor and gear set. Such alignment is accomplished by a precision-machined housing for the motor and gear set or compliant coupling on an output shaft of the motor to an input of the gear set. This arrangement has inefficiencies associated with packaging and is not optimized for typical requirements of such an actuator. More specifically, it is not optimized for power density, performance, and reliability.
Accordingly, it is desirable to provide an electromechanical hinge-line rotary actuator an arrangement of which does not have inefficiencies associated with packaging and is optimized for typical requirements of such an actuator in flight-control applications. More specifically, it is desirable to provide such an actuator that reduces inertia and is optimized for power density, performance, and reliability.